1. Field of the Invention
The present invention relates to an optical apparatus for imaging light from a laser device into a spot shape. Particularly, the present invention relates to an optical apparatus in which the amount of light at the spot will not be changed upon variations of the emitting angle in the laser device.
2. Description of the Prior Art
Recently, lasers are increasingly utilized as essential elements in various instruments such as measuring machines, working machines and so on. The peculiarity of the laser resides in high luminance, monochromatic property and good directivity. It is usual that its own good directivity brings severe requirements for the accuracy of position at which the laser device is set, positional displacement with time and so on. The laser system must meet such requirements. An optical system, for example, an optical system for converging the laser beam may sometimes not be positioned near the laser system. It is general that the platform on which the laser system is placed is interconnected with the optical system through another optical system such as a mirror system or the like. If they are vibrated relative to each other, the apparent emitting angle of the laser beam will vary. It can also be considered that a change in the emitting angle of the laser beam will occur with the passage of time if there is less stability with the oscillation position of the laser.
Referring to FIG. 1, now suppose that a laser system 1 emits parallel rays which are in turn condensed on an object 3 through an optical system 2. The laser system 1 ideally emits a laser beam 10 at its exit end 7 which is parallel to the optical axis. Also suppose that a pin hole 4 having the same diameter as that of the laser beam must be disposed forwardly spaced apart from the optical system 3. If the emitting angle is deviated due to any vibration or change with time of use, the laser beam 11 will be deviated from the pin hole 4 but not condensed on the object 3. In an actual example, the laser system 1 is in the form of 5 mW He-Ne laser and spaced apart from the pin hole 4 by a distance of 1600 mm. If the laser beam of 5 mW is of 0.81 mm diameter and the pin hole is of 0.81 mm diameter, there are obtained 1600 tan .theta.=0.81 and .theta.=1.74 minutes. Therefore, if the emitting angle is changed only through an angle of about two minutes, no part of the laser beam will pass through the pin hole.
Japanese Patent Publication No. 58736/1982 discloses an optical apparatus which can eliminate the adverse affection of the changed emitting angle of the laser beam. In such an optical apparatus, the exit end of the laser system is disposed at a position conjugate with the surface of a light receiving element so that the position of the light incident on the light receiving element will be maintained constant under variations of the emitting angle in the laser system. However, the laser beam incident on the receiving element is divergent.